How about a RAM disk for PS scratch?

[GSimian]

How about the idea of a RAM disk for scratch? I have 1G of RAM, could give 400MB to PS and 450MB to a RAM/scratch disk. Would this be a better idea than my current allotment of all 950MB to PS? Most of my files are in the 50MB size, and I ususally work on one at a time.
Thanks,
George

[Scott W.]

Yes. Using a RAM disk for scratch space will speed things up.

[Jeff Schewe]

Please. . .everybody, disabuse yourself of the notion of using a ram disk for Photoshop. . .ever.

First off, the best, most efficient use of ram for Photoshop is to allocate that ram for the application. End of story.

The current Macs (and I'm assuming you're talking about Macs here) can address 1.5 gigs on the motherboard-even though 4 512dims will fit. However, applications are limited to 999,999k allocations. Which means that the other 1/2 gig can't easily be allocated to applications. However, the OS needs a hefty amount of ram and allocating 999,999k to PS, allowing 100 mbs of so head room for the system will not leave enough unuesed ram to amount to anything substantial for use as a ram disk.

If you have a lot of money to spend, and you want the ulimate hardware for Photoshop, you might consider spending an obscene amout of money to buy a SCSI 2 Fast & Wide solid state static ram drive. If you put a couple of gigs of ram in an enclosure and attach it via a really fast pipe, a solid state ram drive WOULD be a significant preformance booster.

But, to take ram allocation AWAY from Photoshop to allocate a system built ram disk is merely foolish. Allocating 950 MB's and working on 50 MB images won't be improved by subtracting a substantial amount of ram from the allocation for a ram disk.

[Greg Vander Houwen]

Jeeze Jeff, get an opinion will ya ;).

GSimian and Scott,

what he said.

It sounds like a good idea but Scratch should be thought of as secondary to memory. Give PS as much RAM as it can swallow, then point the Scratch to the next fastest thing you've got. Ideally, if you had enough RAM, you would load your system/extensions..., PS, the image and still have enough left over for PS to do everything it needs right in RAM.

btw: Jeff do you know if the old 3-5 times the size, rule of thumb, is still roughly correct? I haven't looked lately.

Greg

[Jeff Schewe]

Greg asked: "btw: Jeff do you know if the old 3-5 times the size, rule of thumb, is still roughly correct? I haven't looked lately. "

The factors of ram allocated to file size have gotten rather complcated. In the old days, the 3-5 was the rule that depended on several factors. 1 undo was a 1x factor, snapshop was 1x factor, pattern was a 1x factor, the file itself was a 1x factor and filling from saved was a 1x factor. So, if you activated all the above buffers, you needed 5x the file size in ram.

But, with the cashing in PS 4.0, you could concievably need even more ram since the screen cache can use both ram and/or scratch. However, since the image cache is non-linear (meaning the image cache doesn't fit the 2x or 2x factoring because each additional cache unit is half the size of the pervious cache unit) and with multi-undo/History since 5.0, the old buffer caching of snapshop and the saved state buffer went away, I have absolutely no clue if the old 3x-5x rule has any meaning anymore.

Personally, I would reccomend people activate their % efficency readout on the lower left window display. If the readout, during the normal course of working on your normal file sizes, ever drops below 100%, you know you don't have enough ram. If it dips into the high 90%'s briefly you're still proably good, but if it ever drops below 90% the preformance of Photoshop becomes way degraded and scratch disk dependent. If you're always at 100% you are good. . .but even then, more ram for Photoshop will increase performance. Bottom line? You can't give Photoshop TOO MUCH ram. . .it'll use everything you give it.

[sPECtre]

Even If you look after those (http://www.computerarts.co.uk/reviews/review.asp?id=335&order=date) expensive add-on cards, you will be limited to the speed our your PCI bus...

We can't wait for faster (hypertransport?) busses!

When asked about an additional coprocessing card (he designed one for mac, long time ago), Chris Cox (one of the Engineers of photoshop) answers:

"Pierre - it wouldn't help.

Most of Photoshop is now bandwidth limited -- the DRAM limits the speed, not the CPU speed. Putting processing on a card would actually slow down Photoshop, because bandwidth to and from the card is lower than bandwidth to and from DRAM.

A co-processing card could only help in a few situations (like median, or lighting effects) where the operation is CPU calculation limited.

Premiere is a different issue - because they have to do compression and decompression of the frames and previewing in real-time.

Yes, PowerShop was that powerful, when it was being sold. But CPUs got faster, DRAM got faster, and the PCI bus didn't. (and AGP generally isn't that fast compared to DRAM)."
(excerpt of Adobe Photoshop User 2 User forum)